Jupiter's magnetic field -- here converted to sound from radio waves collected by spacecraft passing close to the planet -- is the window to its heart. Precise measurements of the magnetic field can reveal details about the planet's interior, such as the size and mass of its core.

That's the goal of Juno, a mission to Jupiter whose launch window opens on Friday. The probe is scheduled to arrive at Jupiter in five years. It'll orbit the planet from pole to pole -- something that's never been done. That vantage point will allow the craft to map the magnetic environment around Jupiter in far greater detail than ever before. And that knowledge will lead to a better understanding of the entire planet.

Scott Bolton is the project's lead scientist.

BOLTON: The real source of Juno is trying to understand the fundamental properties of Jupiter, the state of Jupiter -- what is it made of.

The magnetic field is generated by motions deep below the planet's visible cloudtops. Jupiter probably contains a dense, heavy core surrounded by a layer of metallic hydrogen. These different layers rotate at different speeds, creating a dynamo effect that produces the magnetic field. So measuring the detailed structure and strength of the magnetic field, combined with observations of the planet's gravity, should produce a clearer picture of how Jupiter is put together -- a window to its heart.